Cathodic electropolymerization of methacrylonitrile studied in situ by quartz crystal microbalance, cyclic voltammetry, and impedance spectroscopy

The cathodic electropolymerization of methacrylonitrile was followed with an electrochemical quartz crystal microbalance used in combination with other classical techniques such as cyclic voltammetry, chronoamperometry and impedance spectroscopy. The quartz microbalance has revealed a large adsorption-desorption process of the growing electropolymer on the cathode during repeated cycling. However, a polymer layer strongly bound to the electrode was obtained after several scans, though it is normally soluble in the electrolytic solution. A visible delay between the monomer reduction current and the quartz frequency response was measured during successive sweeps and was found to be dependent on the scan rate. This delay was attributed to the time needed to form a critical polymer concentration in the solution before adsorption. A progressive change in the polymer conformation on the electrode was found during repeated scans. This reorganization process of the electropolymer on the cathode was found to be comparable with the spontaneous adsorption of special polymer chains bearing reactive groups capable of forming chemical bonds with some substrates. These grafted polymers present well-identified structures, called pancake, mushroom and brush. Finally, the behaviour of a polymethacrylonitrile layer swollen by solvent as well as in the dry state suggests a plausible evolution from a mushroom type conformation to a definitive brush conformation during the growth of the electropolymer on conducting electrodes.